Wagner was a fourth-round Draft pick in 2014 out of the University of Utah. He is No. 11 on MLB.com's list of the top 30 Brewers prospects and got the nod over Milwaukee's more experienced young arms by going 5-1 with a 2.01 ERA at Double-A Biloxi. Last year, he was 13-6 with a 1.86 ERA for advanced Class A Brevard County.

"He's pitched well for a really long stretch of time," Counsell said. "He's been on a roll all this season, he was on a roll all last season. He's a guy we think has the best chance to get us a win."

Of the jump from Double-A, Counsell said, "It's not uncharted. Plenty of other organizations, plenty of other teams and plenty of good players have done it. It's experience as much as anything. He's a little newer in terms of the number of innings he's thrown in the Minor Leagues, but his last 200 innings in the Minor Leagues have been really, really good."

Biloxi manager Carlos Subero informed Wagner of his promotion in front of the whole team.

"I wasn't expecting it," Wagner said in comments released by the Shuckers. "I believed I was ready for the moment but you never expect something like that."

He also said, "It's an unbelievable feeling to know how much you have worked to get to this point in your career and everybody that has helped you along the lines. It's a surreal feeling right now."

Wagner played shortstop and pitched in relief at Utah before converting to a starting role in the Brewers' Minor League system. He pitches off a two-seam, sinking fastball.

The Brewers picked Sunday for Wagner's debut over Monday or Tuesday in St. Louis. As a result, Matt Garza and Mike Fiers will each get an extra day of rest before their next start. Garza has been struggling, and Fiers made his last start on short rest.

While Wagner celebrated his promotion, some Triple-A Colorado Springs starters stayed put. Right-handers Tyler Cravy, Taylor Jungmann and Tyler Thornburg were among other potential candidates for a callup after Peralta was placed on the disabled list with a left oblique strain. He will miss 4-6 weeks.

"You earn promotions, and [Wagner] has earned it," Counsell said. "It's not a knock on anybody, it's a credit to him for going out, pitching well and earning it. That's how it works. There's not an order that stays in place, it's changing. Performances change it, and he's performed."

Wagner is expected to arrive at Miller Park on Saturday. The Brewers will probably wait until after that day's afternoon game to formally add him to the 40-man roster, and to make a corresponding move on the 25-man roster.